Environment-friendly vehicles including a hybrid vehicle, a plug-in hybrid vehicle, and an electric vehicle perform charging, discharging, and maintaining control of an auxiliary battery thereof for vehicle fuel efficiency and auxiliary battery protection according to driving conditions and a battery state through variable voltage control of a low-voltage direct current-direct current (DC-DC) converter (LDC). Additionally, LDC command voltage, which is configured to perform charging, discharging, and maintaining control, is determined using mapping work based on the state of charge (SOC) and the temperature of the auxiliary battery.
In a conventional auxiliary battery control method, the auxiliary battery is operated to maintain a mapped maintenance voltage thereof when the SOC of the auxiliary battery reaches a target value, and is operated by a charging voltage when the SOC of the auxiliary battery decreases. Since it is impossible to achieve voltage mapping capable of precisely maintaining a current of 0 A due to the temperature, the degree of deterioration, and the SOC error of the auxiliary battery, the SOC is maintained using continuous charging and discharging based on the target SOC.
In the conventional technology, the charging and discharging efficiency of the auxiliary battery is not 100%, and loss due to a charging and discharging current of the auxiliary battery thus inevitably occurs, thereby decreasing fuel efficiency. In addition, for SOC maintenance and discharge control of the auxiliary battery, the conventional technology requires command voltage mapping and calibration work according to SOCs and temperatures, which requires consumption of a substantial amount of man/hours (M/H). Therefore, a solution for improving fuel efficiency through minimally controlling charging and discharging of the auxiliary battery and reducing M/H required for calibration work is required.
The above description in this background section is merely for improving understanding of the background of the present disclosure, and should not be taken as an acknowledgement indicating that the information forms a prior art that is already known to a person skilled in the art.